Electrocoagulation was already proposed in the late 19th and early 20th century. The use of electrocoagulation with aluminum and iron was patented in 1909 in the United States (Robinson, Australian Water & Wastewater Association, Joint NSW and Victoria State Conference in Wodonga, 22-24 Nov. 1999 (www.electropure.com.au/paper.htm); Vik et al. WaterResearch, volume 18, Issue 1, 1984, pages 1355-1360).
Coagulation is essentially to neutralize or to reduce the electric charge of colloids and hence promote the aggregation of colloidal particles. To destabilize a suspension it is necessary that the attractive forces between particles are greater than the repulsive forces thereof. Attractive forces are mainly Van Der Waals forces, which act at a short distance thereof. In general, the total energy that controls the stability of the energy dispersion comprises attractive Van Der Waals energy of repulsion at short distance, the electrostatic energy and energy due to the steric effect of molecules solvent.
Coagulation can be done by chemical or electrical means. Alun, lime and/or polymers have been used as chemical coagulants. Chemical coagulation is becoming less popular today because of high costs associated with the chemical treatments of a significant volume of sludge and hazardous heavy metals such as metal hydroxides generated thereof in addition to the cost of chemical products needed for coagulation itself. Chemical coagulation has been used for decades.
Although the electrocoagulation mechanism resembles chemical coagulation, although, some differences benefit electrocoagulation. Indeed, electrocoagulated flocs differ from those generated by chemical coagulation. Flocs created with the electrocoagulation process tend to contain less bound water, are more resistant to shearing and are more easily filterable.
Flocs are created during the electrocoagulation water treatment with oxydo-reduction reactions. Currents of ions and charged particles, created by the electric field, increase the probability of collisions between ions and particles of opposite signs that migrate in opposite directions. This phenomenon allows the aggregation of suspended solids to form flocs.
The electrolytic reactions that take place at the electrodes are accompanied by production of micro bubbles of hydrogen (at the cathode) and oxygen (at the anode). These micro bubbles heading up will result in an upward movement of the flocs formed thereof that are recovered at the surface (this mechanism is named flotation).
The complexity of the mechanisms involved in the process of electrocoagulation in the treatment of water is not well scientifically elucidated (Yousuf et al., Journal of Hazardous Material B84, 2001). There are various features of the mechanism of the process and the geometry, or design, of the reactor in the literature. The different physico-chemical treatment, the shape of the reactor and the shape and size of electrodes affect the performance of the treatment. The wide variety of processing parameters reported in the literature and the lack of scientific data for efficient model processing and optimal processing conditions translate into a lack of development in this field. At this time, electrocoagulation is still problematic and therefore not popular (Holt et al., Colloids and Surfaces A: Physicochem. Eng. Aspects 211 (2002); Holt et al., Chemosphere 59(2005) 355-367).
The existence of an electric current in a body of water implicitly requires Faraday reactions surrounding the electrodes. The formation of chemical gradients depends on the electrolytic magnitude. The consequences of chemical reactions become more pronounced and significant in the prolonged application of electrokinetic. The effects include electrolytic of water with the simultaneous development of pH gradients and the transfer of electrolytic dissolution of the anode producing metal ions (Fe3+, Al3+, Mg2+, etc.) or cations of the electrolyte from the anode to the cathode. Chemical reactions can, in ion exchange or precipitation, form new mineral phases for cleaning water for instance.
At the cathode, the main reaction is:4H2O+4e−→2H2+4OH−  (Equation 1)
The increase in hydroxyl ions can increase the precipitation of metal hydroxide. The pH of the cathode's region is basic. The following equations describe the chemical reactions at the anode:2H2O→O2+4H++4e−  (Equation 2)
If the anode is made of magnesium:Mg→Mg2++2e−  (Equation 3)
It is noted that twice as many water molecules are electrolysed at the cathode compared to the anode for the same quantity of electricity.
The struvite is a compound with a little solubility and used as a fertilizer in agricultural fields. This compound is of the formula NH4MgPO4, 6H2O and comprised PO43− and NH4+ ions, both essential to plants growth. Struvite is known as a fertilizer and have been proved potent in soils having a pH between 5.5 and 6.5.
Precipitation of struvite in a wastewater allows the elimination of the ortho-phosphate, NH4+ and magnesium present in the waste water. Currently, processes for precipitating struvite use fluidized beds, or contained tanks reactors. In Japan, the precipitation of struvite has been tested in a sludge treatment reactor. To obtain a good performance, it is essential to optimized both nucleation and precipitation by optimizing the treatment time in the reactor and the nature of the support particles for the precipitation.
Precipitation of struvite is controlled by the pH, the supersaturation, the temperature and the presence of impurities such as calcium and can occur when the concentration in magnesium, ammonium and phosphor ions exceed the solubility product of the complex as per the following expression:Ksp=[Mg2+][NH4+][PO43−]pKs=13.26
The presence of organic matter impact on the nucleation and growth of struvite crystals and reduce the precipitation rate. In a waste water to be treated, NH4+ and PO43− are among the components to be eliminated. While adding Mg2+ in the solution with a basic pH, the precipitate is formed. Several conditions are required for the reaction to occur:                a phosphorous concentration higher than 50 ppm;        a pH value between 7 and 11, preferably between 8 and 9.2;        a molar ratio Mg/P of 0.9 to 1.5;        a strong agitation;        a simultaneous increase in pH and temperature to reduce time of precipitation.Mg2++NH4++PO43−+6H2O→MgNH4PO4.6H2O        
Many patent applications have been filed for the synthesis of the struvite. WO 01/19735 discloses a process for the treatment of manure. WO 95/05347 discloses an electrolytic system using a series of electrodes. WO 2007/009749 discloses a reactor and a method for the production of struvite. U.S. Pat. No. 4,389,317 discloses the chemical reduction of phosphates in water. WO 00/56139 discloses a method for preventing the formation of struvite in fish cans.
WO 2009/102142 discloses a two-steps treatment of an effluent, wherein the effluent is first treatment in an anaerobic reactor followed by a second treatment producing the struvite.
Therefore, there exists a need in the art for an improved method, system and apparatus for optimizing the production of struvite by an electrolytic treatment of a waste effluent over the existing art. There is a need in the art for such a method, system and apparatus for treating an effluent that can be easily installed, economically manufactured and operated. And there is a very perceptible need for an improved method, system and apparatus for treating wastewater over the existing art.